US2679611A

US2679611A - Vapor-arc device

Info

Publication number: US2679611A
Application number: US206434A
Authority: US
Inventors: John L Boyer
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1951-01-17
Filing date: 1951-01-17
Publication date: 1954-05-25
Anticipated expiration: 1971-05-25
Also published as: ES201464A1

Description

J. L. BOYER 2,679,611

VAPOR-ARC DEVICE 3 Sheets-Sheet l May 25, 1954 Filed Jan. 17, 1951 ATTORN EY May 25, 1954 L, BOYER 2,679,611

VAPOR-ARC DEVICE Filed Jan. 17, 1951 5 sheets-sheet 2 O' m j "1 WITNEssEs; 9, INVENTOR John .Boyer.

//f Wj/,a/ A BY WMM /U' ATTORNEY Fig.2.

May 25, 1954 J. L. BOYER VAPOR-ARC DEVICE Filed Jan. 17, 1951 Fig.

Fig.4.

3 Sheets-Sheet 3 1 I3 I4' |05 los s* INVENTOR John L.Boyer.

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ATTRNEY Patented May 25, 1954 VAPOR-ARC DEVICE `lohn L. Boyer, Pittsbur inghouse Electric Cor Pa., a corporation of 33 Claims.

My invention relates to single-anode, pool-type vapor-arc rectiers having a new method and means for initiating the cathode-spot of an are' at the beginning of each conducting period of the device. In one of its broader aspects, my invention is an improvement over the mercuryarc ignitron which is described and claimed in a patent to Slepian and Ludwig 2,069,283, granted February 2, 1937.

My invention is based upon the well-known curves which show the relation between the breakdown voltage and the pressure-distance product pd for various discharge-metal vapors. where p represents the vapor-pressure, in any convenient units such as microns of mercury, and d represents the distance or spacing between the electrodes in any convenient units such as centimeters. While these pressure-distance breakdown curves are different for different discharge-vapors, they all have a common characteristic in showing an extremely high breakdown voltage for small pd values, with the breakdown voltage falling 01T rapidly as the pd value is increased, until the breakdown voltage reaches its minimum value, usually of the order of 200 to 500 volts, at some particular value of the pressuredistance product pd, after which the breakdown voltage again rises, but at a much slower rate, for further increases in the d value.

Unless special voltage-consuming and efflciency-reducing arc-suppressing means are used, a vapor-arc rectifier has to be operated at a pressure-distance product pd which is small enough to make the breakdown voltage high enough to withstand the back-voltage during the non-conducting periods of the device. Usually, this breakdown voltage should be at least 2.5 times the direct-current voltage of the rectier,

more or less, depending upon the circuit-connections, and frequently much higher breakdown voltages are used, to provide an increased factor of safety against backrings.

In accordance with a preferred form of embodiment of my invention, I place the main anode very close to the surface of the pool-type cathode, thus obtaining a small value of the spacing or distance d, and hence a small value of the pressure-distance product pd. I operate the rectier on the initial steep portion of the pci-breakdown curve, so that the two main electrodes will be capable of holding or withstanding a high voltage, Without breaking down the intervening space and forming an arc. In the preferred form of embodiment of my invention, I then provide an auxiliary or starting-anode which has a congh, Pa., assignor to Westporation, East Pittsburgh,

Pennsylvania Application January 17, 1951, Serial N o. 206,434

siderably longer spacing with respect to the cathode, so that the pressure-distance product pd for the auxiliary starting electrode approaches more closely toward the minimum-breakdown value, so that the long gap between the auxiliary starting electrode and the main cathode has a relatively low breakdown voltage, and is thus fairly easy to break down by the application of a suitably timed momentary voltage-impulse. It is sometimes necessary to provide some sort of means for shielding the auxiliary starting electrode against breakdown between itself and the main anode, and sometimes this shielding may suce without the increased spacing of the starting-anode.

Tests have indicated that my new arc-initiating means for a make-alive type of vapor-arc rectifier is in many respects greatly desirable over the ignitor-means which was shown in the Slepian-Ludwig patent, and which has been in use ever since, consisting of a high-resistance or semiconductive body which dips down into the mercury-pool, and which usually requires a rather considerable amount of exciting-current for anything like reliable operation.

My invention can be rused with any one of several discharge-metals for forming the vaporizable reconstructing cathode-material, including any metals capable of forming a liquid pool at a reasonable temperature, and also having the necessary low-arc-drop characteristics. The best known discharge-metals of this type includemercury, cadmium, and the three heavier stable light metals of the alkali-metal group, ing cesium, rubidium and potassium, as more particularly described and vclaimed in a copending joint application of August P. Colaiaco and myself, Serial No. 144,354, led February 15, 1950. As explained in the rst paragraph of said copending joint application, these three alkalimetals, cesium, rubidium and potassium, form a more or less distinctive class by themselves, which may be described as the alkali-metals having four, five and six shells in their atomic structures, or the stable alkali-metals having more than three shells in their atomic structures.

My novel excitation-method is particularly significant in connection with alkali-metal tubes, of a type using a pool-type vaporizable reconstructing cathode-material consisting of Veither cesium, rubidium or potassium. By a pool-type tube or valve, I mean any tube or valve in,which the active cathode-material is both vaporizable and reconstructing. It may be either an open pool, or a sponge-held pool in which a porous comprissubstantially non-vaporizable material holds at least the active portion of the vaporizable reconstructing cathode-material, or an open-pool having therein many vertically disposed baies which are spaced by distances larger than the capillary dimensions which distinguish a sponge-like material. My new excitation-method makes it practically possible, for the first time, to construct a single-anode pool-type alkali-metal tube, because the previously known semiconducting ignitormaterials have not been usable in contact with the extremely chemically active alkali-metals, cesium, rubidium or potassium, which wet almost anything, and soak up into the pores of the ignitor.

Heretofore, alkali-metal rectifier-tubes have been of the hot-cathode type, as. shown, .for example, in the previously mentioned application of Colaiaco and myself. These tubes have been not only relatively expensive to make, and slow to heat up in the initial process of getting the tube into operation, because ofthe relatively high temperature of the cathode, but they have been distinctly limited in their output, because of the necessity for continuously carrying a monomolecular layer of the discharge-metal to the heated cathode through the medium of a vapor of the discharge-metal.

In ahot-cathode type of alkali-metal tube,

there has also been the necessity for interposing heat-shields between the relatively hot cathode and theclosely spaced relatively cool anode, and these heat-shieldshave not only been a source of considerable expense and difficulty, but they have inevitably increased the arc-drop within the tube. These hot-cathode alkali-metaltubes have also had an internal arc-drop or voltage-loss which is` widely variable under different loadconditions. Apool-type tube, on the other hand, is'capable of carrying tremendous or almost unlimited currents on-a relatively low surface-area of the cathode, so that the size and cost of a tube of any given rating is very much less than that of ahot-cathode tube, and moreover the arcdrop of a pool-type tubeis almost constant with varying load-conditions.

Other features of 4my invention involve various structural details, temperature-controlling details, and other features such as the possible use of a beryllium or titanium coating on the anode, and, if a grid-is used, on thegrid also, or on the grid alone,.for the purpose of permitting these parts `to run-hotter' without substantial electronemission.

With the foregoing and other objects and distinctive features in view, my invention consists in the structures, circuits, systems, combination, parts, andmethods of designand operation, hereinafter described and claimed, and illustrated in the accompanying drawings, wherein Figure 1 is a vertical cross-sectional view' of a preferred form of tube-structure embody-ing some ofthe features of my present invention;

Fig. 2 is a diagrammatic view of circuits and apparatus involving a complete installation using three of my novel tubes to supply a direct-current load from a three-phase source of supply, with the necessary excitation-control and temperature-control features; and

Figs. 3, 4 and 5 are somewhat diagrammatic cross-sectional views of other forms of tubes embodying different features of my invention.

As shown in Fig. 1, my novel rectifier-tube is an asymmetrically conducting vapor-arc device which comprises an evacuatedcontainer Shaving two, and only two, main electrodes 1 and 8 therein. The main metallic portions of the evacuated container 6 (as distinguished from the insulator or insulator-seal portions thereof, which will subsequently be described), are preferably made of iron or steel, although other metals could be used. Each tube thus constitutes a single-phase rectifier, for interchanging power between two circuits, such as an alternating-current circuit, and a direct-current circuit. In Fig. 2, the alternating-current circuit is illustrated as a three-phase supply-circuit Ill, and the direct-current circuit is indicated as a direct-current loadcircuit II; and a separate rectifier-tube 6 is used for each ofthe three phases of the supply-circuit I0.

Each tube 6 is also provided with an auxiliary starting-anode I2, for the purpose of exciting the tube at the beginning of each conducting-period of the two main electrodes l and 8. In accordance with my present invention, the cathode 8 is a pool type-of cathode, and hence it is necessarily disposed below the main anode 1, so that it is the lower one of 8. TheAcathode-pool I3 consists of a vaporizable reconstructing cathode-material as hereinabove defined, which is preferably selected from the group comprising mercury, cadmium,` cesium, rubidium and potassium, and which` still more preferably is selected from the previously mentioned alkali-metal group comprising cesium, rubidium and potassium, with particular emphasis on cesium as the vaporizable reconstructing cathode-material.

As will be described in connection with Fig. 4,

this cathode-pool I3Y may be an open pool, but it is preferable, for a number of reasons, that the pool-material, or vaporizable reconstructing discharge-metal, should be held by a porous substantially non-vaporizablematerial in the form of a sponge or partition-filled structure with spaces of capillary dimensions between the partitions, as indicated at I4 in Fig. l. This porous material-can be one of the high-temperature conductors, such as molybdenum, tungsten, tantalum, ruthenium or carbon. The dischargemetal` I3` saturates the cathode-sponge I4, but if there is-a small amount more than necessary, it can collect in the space around the rim of the sponge, or in any other suitable space which might-be provided. In some cases, as indicated in Fig. 1, it may be desirable to retain the'cathode-sponge I4 by means of clips I5, which hold the sponge in place and raise it slightly off of the bottom of the cathode portion of the container 6, so` that the liquid discharge-metal I3 may getV in underneath the sponge and more readily distribute itself throughout the massA of the sponge.

It is necessary that the discharge-metal I3 should wet the sponge, so that it will fiow readily through the capillary spaces thereof. When mercury is used as thevaporizable cathode, the sponge has to have. a preliminary treatment with hydrogen at a high-temperature, in order that the mercurymay wet the sponge-material readily, but when-either cesium, rubidium or potassium is used, it is not necessary to preliminarily treat the sponge, since these alkali-metals wet other materials so easily.

Asshown in-Fig. ll', it may' also be desirable, at-'times, tosurroundthetop edge of the cathodesponge `I4'-with aninsulating washer I5, which maybe held-by-clips-If'l, inorder to prevent the the two main electrodes 1 and cathode-spots from running off of the spongecathode.

The main anode 1 and the auxiliary startinganode I2 have to be separately insulatingly supported so that both are spaced and insulated from each other, and from the cathode 8. In the form of embodiment of my invention shown in Fig. 1, both of these insulating supporting structures are a part of the evacuated container 6. Thus, the main anode 'I is separated from the main cathode 8 by a glass-metal seal I8, I 9, 25J, in which thin metal spinnings I8 and 20 are sealed between a tubular glass member I9 and the main anode and cathode structures l and 3, respectively. When a chemically active discharge-metal is used, such as cesium, rubiclium or potassium, the metal spinnings I8 and 20 of the seal should be plated internally with either titanium or zirconium, or perhaps with beryllium, or even chromium, as described in the aforesaid application of Colaiaco and myself, in order to prevent the reduction of the oxides of the glass by the chemically active discharge-metal when the tube is up to the correct operatingtemperature.

In the preferred form of embodiment of my tube, as shown in Fig. 1, `the upper main electrode or anode 'I has a hollow or tubular re-entrant portion 22, which extends down into the device from the top of the container. The active portion of the main anode 'I is a at metal piece 'l which is secured to the bottom of the re-entrant portion 22. This active main-anode portion I is provided with a central hole 24, which is sealed to a starting-anode glass-metal seal-

portion

25, 26, 27, which extends up like a closed-top chimney, extending up from said hole 25, and capped, at its top, by the auxiliary starting-anode I2. The thin metal spinnings 25 and 21 may be sealed between the tubular glass member 26 and the metal portions I2 and 'l' respectively, in a manner already described in connection with the main glass-metal seal I8, I9, 20.

In any vapor-electric discharge-device, the vapor-pressure p is determined by the condensation-temperature of the vapor, which is the lowest temperature of any internal-wall portion of the device or tube. In pool-type tubes, 1t is usually more convenient to make the coolest spot or region somewhere on the cathode-portion 8 of the evacuated container 6, that is, the portion of the evacuated container which carries the cathode-pool I3. In would be possible, of course, to make some upper portions of the containerstructure, such as the main-anode portion l, the coolest spot in the tube so that the condensation of the discharge-metal vapors would take place there, but in such a case, it would be necessary to design the insulator I9 so that the drops of condensate would not flow in a steady stream across the insulator so as to short-circuit the same. It is usually desirable, therefore, in my pool-type tubes, as in previous pool-type tubes, to make some portion of the main cathode structure the coolest point in the tube, which determines the vapor-pressure p of the tube.

In a preferred form of embodiment of my invention, as shown in Figs. 1 and 2, I prefer to go further, and make the bottom of the cathode container portion 3 the coolest point in the tube. More specifically, I prefer to make the cathodepool I 3 the coolest part of the tube, except, of course, for the portion of the cathode-pool in the vicinity of the cathode-spot or arc-terminal.

To this end, it is desirable to use a cathode sponge I4, and to make the sponge as thin or shallow as possible, so as to reduce the depth of the cathodepool I 3 and thus reduce the temperature-gradient between the top of the pool and the coolest point, which is the bottom of the cathode-portion 8 of the evacuated container 6. In this way, I use a cooling system in which the heat is dissipated mainly by conduction through the cathode-pool, this heat being carried down to the bottom of the container, and thence radiated to a suitable cathode heat-radiating surface.

When a sponge I4 is used, the pores of the sponge serve to hold the cathode-material in place, and to replenish it as it becomes evaporated oir in the arc, and it is thus possible to use a more shallov.r cathode-pool I 3 than would be possible if an open-pool construction were used. In some other, or previously known, forms of tubes, the cathode-pool has not been the coolest place in the tube, so that condensation occurred somewhere else, such as on the side walls of the cathode-portion 8 of the evacuated container 6, and hence the cooling of the cathode-pool was obtained by evaporation of the pool-material, as distinguished from conduction through the cathode-material to the coolest-point wall-surface therebelow, as in my preferred construction.

Where a costly discharge-metal is used for the cathode-material, such as cesium or rubidium. or even potassium, it is desirable to use a thin cathode-sponge Id, not only to keep the cathodepool I3 thin or shallow, but also so that the sponge will occupy some of the space of the thin or shallow pool, thus requiring a minimum amount of the cathode-material. With increased demands for such cathode-materials, such as cesium, the cost, however, will be quickly and materially reduced, so that deeper pools, and hence thicker or deeper Sponges, may be utilized. In the case of a thick sponge, whatever may be the cathode-material, it may be desirable to use Sponges in superimposed layers, having diiferent porosities, and possibly even having different melting-points, with the material having the iinest pores and the highest melting point at the top where it may be played upon by the arc, as has been previously suggested in other structures.

In all vapor-arc devices, there is a certain optimum range of vapor-pressures in which the arc-drop is a minimum, and the coolest spot temperature is generally so chosen as to make the vapor-pressure fall within this optimum range. This optimum vapor-pressure, whatever may be the discharge-metal, seems to lie somewhere within the pressure-range between 10 and 80 microns of mercury. For example, if cesium is the discharge-metal, a condensation or coolestpoint temperature of C. will produce a vaporpressure of 41 microns. If rubidium is the discharge-metal, the corresponding condensationtemperature will be 204 C., and for potassium the corresponding temperature is 245 C. This discussion of optimum vapor-pressures, for obtaining the lowest voltage-drop within the arc, that is, from the main anode 'I' to the top of the cathode-pool I3, is limited to pool-type rectiers, as distinguished from the hot-cathode alkalimetal rectiers which are described and claimed in the previously mentioned application of Colaiaco and myself, wherein the necessary vaporpressure was determined by the necessity of having a suflcient vapor-density to maintain or replenish the monomolecular layer of dischargemetalon the heatedsurface of the cathode during heavy-current load-conditions.

In common with other single-anode rectiiers, such as the ignitron of the Slepian-Ludwig Patent 2,069,283, it is a-characteristic of my present invention that the tube carries current, in the form of an arc between the two main electrodes 1 and 8, or 1 and I3,-onlyY while the main anode 1 is positive with respect to the cathode 8, and it is a further characteristic of the device that this main current-carrying arc has to be started by some sort of auxiliary starting-anode means which creates the initial cathode-spot on the cathode-pool I3, and thus permits lthe main arc to strike between thetwo main electrodes. This initiating arc-establishing function has to be repeated at the beginning of each conducting period of the tube, and this is commonly done by the application of a suitable exciting or startingvoltage to the auxiliary starting-anode at the moment when it is desired to initiate a conducting period of the tube.

My auxiliary starting-anode I2 is no exception, insofar as the necessity for applying a suitable excitation impulse thereto is concerned, although my auxiliary starting-anode I2 is exceptional, in being initially spaced from the cathodepool I3. When the activating or exciting impulse-voltage is applied to my auxiliary startinganode I2, it is necessary that some means or expedient shall be provided for determining where the gap-breakdown takes place, and for making sure that this gap-breakdown from the auxiliary starting-anode shall always terminate on the vaporizable cathode-material in the pool I3, as distinguished, for example, from terminating on the anode 1, or on the side walls of the evacuated container 6, or on any other spot other than the cathode-pool I3.

In Figs. 1 andY 2, I have shown an insulating shielding barrier-means in the form of a separate tubular heat-resistant ceramic or glass insulator 30 Which surrounds the hole 24 in the active main-anode portion 1. This insulating tubular shield 30 thus acts as an extension of the insulating tubular part 26 or" the glass-metal seal-structure which supports the starting-anode I2, so that any discharge which constitutes the beginning of a gap-breakdown from the starting anode I2 to any other conducting portion of the device will be constrained to travel downwards through the two insulating tubes 26 and 3D, to a point which is so close above the top of the cathode-pool I3 that the gap-discharge will terminate there, rather than anywhere else.

This gap-breakdown discharge usually starts as a glow-discharge, because of the great electrode-separation, and this causes a sufficiently high positive-ion bombardment of the cathodepool I3 so that it very quickly changes into a cathode-spot, in something like three-tenths of a millisecond, more or less. Once this cathodespot has ben formed, the main anode 1' practically instantaneously picks up current, by establishing an arc to that same cathode-spot, which instantly spread over to other portions of the cathode-pool I3, and thus the main anode 1 begins to carry whatever current is required by the load-circuit II (Fig. 2).

In common with other arc-type dischargedevices, my improved tube operates well up on the steep portion of the breakdown pd curve, where the breakdown voltage is quite high, and the pressure-distance product pdis quite considerably smaller than the value which would produce the minimum breakdown voltage between the main anode 1 and the main cathode 8. It,

of the non-conducting period of the tube, and.v

usually some factor of safety is allowed.

In practicing my present invention, I prefer to make this pressure-distance product pd, which is applicable to the main anode, very exceptionally small, so that the arcing distance d which separates the main anode 1 from the main cathode 8, shall also be small, thus reducing the arc-drop during the current-conduction period of the tube. In fact, as shown in Fig. 1, I prefer to make the main-anode spacing d small enough so that operational difficulties would have been encountered due to droplets of the cathode-pool material iiying up and striking the active anodesurface 1 and thus forming cathode-spots on the anode, if it were not for the restraining effect 0f the capillary pores in the cathode-sponge I4 which I prefer to use.

Itis well known that such cathode-metal droplets, in contact with the anode of a tube, will cause backiires, or tube-conduction during the negative half-cycles of the anode-voltage. at which times no tube-conduction is desired. It is also known that a cathode-sponge, or other porous material, restrains the upward splattering of these droplets of cathode material, and thus obviates the necessity for increasing the anode-spacing d or interposing various shields and barriers and protective grids, such as are known in the art, and all of which increase the voltage-drop which occurs 'within the tube during its normal operation. This is an additional reason why I prefer to use a porous material such as the cathode-sponge I4, in addition to the other reasons which have already been described, and the still further reason which will now be described in connection with the relative lengths of the spacings of the main anode 'I and the starting-anode I2, with respect to the cathode B.

It will be recalled that it is necessary to provide'some sort of breakdown-determining means for making sure that any. gap-breakdown from the auxiliary starting-anode I2 shall always terminate on the cathode-pool, rather than on any other spot within the tube. In the preferred form of embodiment of my invention, which is shown in Fig. l, an essential par-t of this breakdown-determining means resides in a structural arrangement in which the effective gap-spacing d from the auxiliary starting-anode I2 to the cathode is considerably larger than the effective gap-spacing d between the main anode 1 and the cathode. This makes the pressure-distance product pd for the auxiliary starting-anode I2 larger than the corresponding product pd for the main anode 1. Thus the value of the pd product, as applicable to the starting-anode, is much larger than for the main anode, which means that the starting-anode I2 has a much smaller breakdown-voltage than the main anode 1. Thus, whereas the main anode 'I is designed so that it will never spontaneously break down its gapseparation d with respect to the cathode 8, the auxiliary starting-anode I2 is deliberately deigned so that it will more readily break down its gap-spacing d to the cathode, when a suitable positiveV voltage applied to said startinganode, to start a discharge from said startinganode to the cathode-pool.

The starting-voltage which is applied to the auxiliary starting-anode I2 may be either larger or smaller than the maximum voltage which is applied to the main anode I during the course of the operation of the tube. The pressuredistance product pd which is applicable to the auxiliary starting-anode I2 will usually be less than the optimum pd value corresponding to the minimum breakdown-voltage, but it may obviously be made equal to this optimum pd value, or even larger than said value, so long as the breakdown voltage of the auxiliary-starting anode I2 is less than the starting-voltage which is applied thereto for the purpose of initiating a period of conductive operation of the tube.

The phenomenon just described is thus another, and extremely important, reason why it is desirable to have an unusually small electrodeseparation distance d for the main anode l, so that the electrode-spacing d which is applicable to the auxiliary starting-electrode I2 may be relatively considerably longer, thus relatively decreasing the ability of the starting-anode I2 to withstand applied voltages without a breakdown. Thus, I relatively increase the ability of the starting-anode to break down, with reasonable values of applied voltage, at vapor-pressures which are not too great for the proper operation of the main anode. In other words, I want the starting-electrode I2 to break down its gapspacing to the cathode i3, but I do not want such a breakdown to occur in the case of the main anode l. This greater gap-spacing of the starting-anode I2 is thus an important addition to the shielding-effect of the tubular insulating shield 30, in determining the breakdown-path from the auxiliary starting-anode I2y and causing that path to always terminate on the cathode-pool in preference to any other spot within the tube.

In fact, the long-gap starting-anode construction is so important that, in many cases, particularly where the rated voltage of the tube is relatively small, this long gap-spacing of the starting-electrode is itself sufficient to cause the breakdown-discharge of the starting-electrode always to terminate on the cathode-pool, without any particular shielding-means to this end,V

provided that the internal geometry or spacings within the tube are favorable.

As shown in Figs. 1 and 2, however, I prefer, in many instances, to use both the long-gap starting-electrode construction, and the insulating barrier type of shielding 3U, and also, in addition, an electrostatic type of shielding in the form of a cathode-potential cylindrical conducting shield 3| around the lower portion of the insulating supporting structure 25-26-21 which supports the auxiliary starting-anode I2. Such a cathode-potential shield 3i protects the auxiliary starting-anode l2 from receiving a potential-gradient from the main anode l, and thus assists in preventing a gap-breakdown between said auxiliary starting-anode I 2 and said main anode l due to the operating-voltage which is applied between the main anode l' and the cathode il.

The essential parts of a complete three-phase system, using three tubes 6 of the type just described, is shown in Fig. 2. Current from the three-phase supply-line Il! is fed to the three main anodes 'i through a transformer 33, in any of several well-known ways. The three cathodes 8 are connected to a common cathode-circuit 34, which constitutes the negative terminal of the direct-current load II. The positive terminal of the direct-current load is the secondary neutral of the main transformer 33.

An exemplary excitation or ming-system for the starting-anodes I2 consists essentially of a firing transformer 36, which is energized from the polyphase supply-line I0, and charges three firing-capacitors 3'! through charging-rectiers 38.l The respective firing-capacitors 31 are discharged, at suitable times, to the respective starting-anodes I2, by means of grid-controlled tubes 3S which are provided with a suitable phasecontrolling means 40 for controlling the portion of the cycle in which each of the tubes E is started or fired, thus controlling the output-voltage of the rectifier-assembly. This is only one of several suitable firing-circuits which could be used for the single-anode rectiers 6.

Usually, it is desirable to provide, also, some sort of sustaining keep-alive means for keeping the main rectier-tubes 6 from going out under very light load-conditions in the direct-current load-circuit II. A suitable means for this purpose could include a line-energized low-voltage transformer 43, the secondary terminals of which are connected to the three starting-anodes I2 through suitable isolating-rectifiers 44.

While I am not limited to any particular design with respect to voltage-requirements and other quantitative retails, it may be mentioned that, if the main rectifier-tubes 6 are designed with a main-anode spacing d of from 1 cm. to 1.3 cm., and if the starting-anode spacing d is of the order of 13 to 25 cms., it would be appropriate for the nring transformer 35 to have an outputvoltage of the order of 3,000 volts, which would provide a very comfortable margin of safety which would make very sure of prompt and certain ring, while the sustaining-voltage transformer 43, if used, might have .an output-voltage of something like 55 volts. The direct-current voltage-rating of the rectifier-system could be almost any voltage, either higher or lower than the 3,000-volt starting-circuit, being limited only by the breakdown voltage of the main anodes 1, which is very high because of the small mainanode spacing d. These figures are only exemplary.

The temperature-controlling means for the rectier-tubes lIi is illustrated, by way of example. in Fig. 2, as comprising an insulated cubicle 50, which houses all three of the rectiers 6, as well as a blower 5I, and a Ventilating passage 52 having inlet and

outlet ports

53 and 54, respectively, as well as damper-

valves

55 and 56, the valve 55 being used for closing the outlet-port 54, while the valve 56 is used for closing the portion of the Ventilating-passage between the tops of the rectil'lers 5 and the intake-opening of the blower 5I The bottom of the main cathode 8 of each of the rectiers 6 is cooled by means of a cathoderadiator 60?, which is bolted up against said cathode-member 8, and which is provided with suitable heat-radiating vanes 62.

The main anode 'l of each of the rectifier-tubes E is cooled by means of a cylindrical baie 64, which extends down into the re-entrant anodestructure, so that the cooling-fluid (whether gas or liquid) will enter over the top of each rectiertank 3, being then directed downwardly, by this anode-baille cylinder 64, to the active main-anode portion T at the bottom of the anode, after which the cooling-duid is 'discharged upwardlyout of the rectier-tank.

As shown more particularly in Fig. 1,-the top surface of the active main-anode portion 1', which is made of steel, is secured, as by bracing. in intimate thermal contact with the bottom of a massive copper plate or washer 61, which is also provided with a hole 58, corresponding to the anode-hole 24. Secured within the hole 63 is an upstanding chimney or cylindrical barrier '69, AWhich provides a guiding-means for carrying the cooling-fluid upwardly out of the rectifier, after it has Cooled the active'anode-portion 'l'. This chimney or cylindrical barrier 69 also keeps the cooling-fluid off of the auxiliary starting-anode glass-metal seal-

member

25, 26, 21, as will be subsequently explained. The previously described intermediate cylindrical anodebafe 64 is preferably also made of copper, and is provided with copper heat-radiating fins 14 (Fig. 1). The'bottoms of the fins 15 are integrally secured to a massive copper bottom-plate or washer .15, `which is removably secured, by many copper bolts v16 (for good heat-transfer) to .the top of the copper washer 61 which forms an integral top--portion for the active main anode 1.

The blower 5I,-as shown in'Fig. 2 blows air (or other cooling-fluid), through an opening 11 in a horizontal partition-plate `'13, and thence to a space under the bottoms of each of the three rectifier-containers 6. Each of these rectifiertanks 6 is supported concentrically within an individual outercylindrical ,chimney-member 19, which is spaced from vthe side-walls of the respective tanks 6, so that each outer cylindrical chimney-member 19 guides the Ventilating-fluid upwardly to vthe top of the rectier-tank, after rst passing over the cathode radiator-fins 62 and thus making the bottom of the cathode 8 the coolest point in the tube. The-tops of the

cylindrical members

19 and 64 of each vrectifier-unit are joined by a washer-like insulating barrier 8i, so that the cooling-fluid is constrained to flow downwardly into the anode, between the

cylindrical portions

64 and 22, so that it cools the active anode-portion 1'., after which the coolingfluid is discharged upwardly andfout of the rectier-tank, iowing between 'the

cylindrical members

64 and 69, as shownby the arrows'in Fig. 2.

The cooling-huid which is supplied to the rectier-tanks 6 by theblower 5| is either recirculated through the Ventilating passage 52, or drawn in through the Ventilating-inlet 53 and discharged through the outlet 54 of the-housing 5D, dependent uponthe positions of the dampervalves y55 and 56. Thesedamper-valves are indicated, diagrammatically, as beingconnected together and to a valve-operating. motor 83, in such mannerl that when one of these valves isclosed, the other is opened. When the outlet-controlling valve 55 is open, a maximum-cooling effect yis obtained, because the blower 5I draws in outside air through the inlet 53; but when the outlet-controlling valve 55 is closed, there is an internal recirculation of the cooling-duid, so that there is substantially no cooling-eiect of the recirculated air. At intermediate valve-positions, intermediate cooling-eiects are of course obtained.

It is usually desirable to automatically control the cooling-effect, in order to hold the respective cathodes 8 at the desired operating-temperature, or within a desired temperature-range. For this purpose, by way of example, I have indicatedzeach of the cathode-radiators 68 as being provided with a thermal element in the form of a bimetallic contacter 85, which moves either to the right or to the left to `energize the valve-operating motor 33 in the one direction or the other, as may be necessary to control the cathode-temperature.

Before the rectier-instal1ation can be initially put into use, the various parts must be rst heated up to their-necessary temperatures, which are above the ordinary room-temperatures. For this purpose, I have shown three sets of electric heaters, all of which may be energized from a suitable phase or phases of the low-voltage transformer 43, or from any other suitable source.

First, there is a group of air-stream heaters `86, for heating the circulated cooling-fluid Yduring the initial warming-up period, and also possibly at light-load periods. These heaters `86 could be at any convenient place within the airstream, being shown as being disposed between .the several rectifier-tanks 6 and their respective outer chimneys 19. .By way of illustration, I have shown an overcurrent type of load-responsive vrelay 81 for deenergizing the air-stream heaters .86 in response to a predetermined magnitude of the direct current in the load-circuit l l.

The second and third types of heaters which -I'use are-heaters for maintaining a sufficiently high temperature on each ofthe insulating sealrnembers le and 26. Thus, a group of mainseal heaters SS are disposed in close proximity around the main-seal insulators `IS) of the respective rectiiier-tubes; while a helical heater 89 is slipped down over each starting-anode structure, so as to be in close proximity to the starting-structure seal-insulator 26. It will be noted that the starter-seal heaters 8S are separated from the cooling-air streams-by the inner anodechimneys 69. Both of the seal-heaters 88 and vSe may be left permanently in service, if desired, whenever the rectiers are in service. They are for the purpose of making sure that the dis charge-metal does not condense on the sealinsulators I9 and 25. In the illustrated form of embodiment of my invention, as shown in Fig. 2,

the main--seal heaters 88 are surrounded by an .insulating guard 9B which protects them from .the coo1ing-air stream.

In the operation of the cooling system as above described, the cooling-air passes 'irst over the cathode-cooling ,fins or vanes 62, so that the main cathodes 8 are the coolest parts of the respective tubes. The cathode-fins 62 partially heat the cooling-stream, so that the streams which cool the main anodes 1 hold said anodes at a temperature slightly higher than the bottoms of the cathodes 8, which is desirable, in order to prevent condensation of the discharge-metal vapor on theanodes.

In the electrical system, as shown by way of example in Fig. 2, it will be noted that the secondary star-point of the firing-transformer 36 is connected at 92 to the secondary star-point of the low-voltage transformer 43, and this point is also connected, by a conductor 93 to a returncircuit 94 for the seal-heaters 88 and 89, this return-circuit being connected, at 95, to the common cathode-circuit 34. It is to be noted that the electrostatic conducting shields 3l, near the bottoms of the respective starting-anode supporting-

structures

25, 26, 21, are also connected to the seal-.heater return-circuit 94, so as to be at the cathode-potential. It is believed that the other circuits, and the electrical operation of the entire system, will be apparent from the diagrammatic circuits indicated in Fig. 2

13 and from the explanations which have already been given.

The foregoing descriptions of a preferred structure and arrangement are intended to be understood only in an exemplary sense, as my invention is obviously not limited to these particular details. By way of example, several illustrative alternative structures are shown in Figs. 3, 4 and 5.

In Fig. 3, my invention is shown embodied in a grid-controlled tube, in which a grid 96 is disposed between the main anode 1 and the main cathode 8, the main-anode spacing d being necessarily made somewhat larger than in the gridless tube of Fig. 1. As described and claimed in a companion application of R. JN. Ballard and myself, Serial No. 205,899, filed January 13, 1951, patented July 29, 1952, No. 2,605,439, the grid 96 is preferably mounted in good thermal contact with a separate metallic grid-supporting wall-portion 91 of the evacuated container 6, being dispose-d between the main glass-metal seal I8, i9, 20, and a grid-to-

cathode seal

91, 98, 99. In Fig. 3, the previously described separate insulating shield 30, which constrains the starting-anode breakdown to occur to the cathode-pool I3, in preference to any other portion of the rectifier, is shown, by way of example, as being an integral downwardly projecting extension of the glass starting-anode insulator 26, as shown at 30'. It extends down, in spaced relation, through a. hole I in the grid 96.

The inner or inside surfaces of the grid 96 in Fig. 3, and of the anodes 'I and l2 of either Fig. 3 or any other form of embodiment of my invention, and in fact any metal internal-surface portion of my device, other than the active part of the cathode-pool, may sometimes, with advantage, be coated with some suitable metallic coating of low electron-emissivity, the only known exceptionally good examples of metals of this class being beryllium and titanium. Such a surface or surface-coating would make it possible to operate said parts at a higher temperature, without producing enough electron-emission to cause backres. In this respect, the pool-type tube of the present application is different from the hot-cathode alkalimetal tube of the application of Colaiaco and myself, because, in a pool-type tube, even though some of the berryllium or titanium should volatilize off, in time, at the high operating temperature of the anode or grid, any recondensation of the beryllium, or possibly also the titanium, on a pool-type alkali-metal cathode would do little or no harm, because it would boil 01T at the cathode spot, whereas, in a hot-cathode tube, any beryllium, and possibly also any titanium, which became deposited on the heated cathode, would still further impair the difficultto-get electron-emissivity, which is already a disadvantage of the hot-cathode tube as compared with the pool-type tube. Of these two emissivity-depressing coating-metals, namely, beryllium and titanium, titanium has an advantage because of of the extreme personneldanger which is involved in handling beryllium.

Fig. 4 shows a form of embodiment of my invention in which a plain or open cathode-pool |3 is used, that is, a pool without the cathodesponge |4 of Figs. 1, 2 and 3. Since an open pool is used, suitable baie-means must be provided for preventing the droplets of the poolmaterial from reaching the anode 1; and hence, again, the main-anode spacing d must be made 14 larger than in Figs. 1 and 2. In the baiiling arrangement shown in Fig. 4, three bales are used, namely, an upper metallic washer-like bale |02 which is carried by the side walls of the cathode-portion 8 of the container 6, this baffle being disposed close under the main anode Next below the metal baiile |02 is an insulating barile |03 which extends out as an integral ani nular ring-shaped formation from the downwardly extending insulator-portion 30. The third and lowermost baille which is shown in Fig. 4 is an insulating washer |04 which is supported, close above the cathode-pool |3', from the side walls of the cathode-member 8. It will be understood that any suitable baffle or shielding means could be used for protecting the main anode of Fig. 4 from the droplets of the pool-material.

In Fig. 5, I show a modified form of embodiment of my invention in which the previously described auxiliary starting-anode |2, instead of being supported above the active top surface of the cathode-pool |3, as in the previous forms of embodiment, is disposed below said pool, as shown at I2'. In Fig. 5, I provide a cathode-sponge I4' which rests fiat against the bottom 8' of the cathode-portion 8. Both the sponge lll' and the bottom 8' are provided with central holes |05 and |06, the latter being larger than the former, and the starting-anode glass-metal supporting-shield structure 25', 25', 2l' extends down below the cathode-bottom 8', around the hole |05, so that the auxiliary starting-anode |2 is at the extreme bottom end of the structure. The capillary pores of the cathode-sponge I4', in Fig. 5, prevent any substantial leakage of the molten cathode-metal down through the hole |05 in the cathode-bottom 8', but if there should be any such leakage, the molten material would be promptly evaporated again, because the starting-anode seal-portion 25', 25', 21' necessarily has to be kept at a sufliciently high operating-temperature, so that no molten or condensed cathode-material may be formed or remain thereon, as previously described. While this arrangement, as shown in Fig. 5, has the disadvantage that a relatively long rectifiertube is required, it has the advantage of a much simpler anode-structure, in which the central anode chimney-member 69 of the other gures can be omitted, and a better cooling and temperature-control can be maintained on the anode.

While I have described and illustrated my invention in several dilTerent structural forms of embodiment, and while I have illustrated a suggestive circuit-arrangement, a suggestive coolingsystem, and exemplary degree-limitations of temperatures, spacings and voltages, I wish it to be understood that my invention is not limited in these respects, beyond the essential features which have been pointed out in the description and which are recited in the appended claims. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

l. As a symmetrically conducting vapor-arc device comprising an evacuated container having two, and only two, main electrodes therein and also having an auxiliary starting-anode therein, the operating portion of one of said main electrodes including a vaporizable reconstructing cathode-material, the operating portion of the other onev of said main electrodes including an active face-portioncomprising the active main anode of the device, means for separately insu- -latingly supporting said main anode 'and said .starting-anode vso that bothare-spaced and insulated from each other and from'the cathode,

and breakdown-determiningmeans comprising structural.arrangement in which the `insulating supporting-means ior :themain anode causes the effective spacing d between the active main-anode portion and the operative portionof Vthe vaporizable cathode-material to be small enough to make 'the pressure-,distance product pd consid- Ierably smaller' than the rpci product corresponding to theminimum breakdown-voltage of the vaporizable reconstructing :cathode-material, where p is the operative vapor-pressure of thedevice, and

alsosmall enough tonormallyr prevent a restriking of an arc between the two 'main electrodes during the non-operating periods of device, and further characterized by theinsulating supporting-means for the starting-anode causing thefeiective spacing between said starting-anode and the operative portion of the vaporizable cathode-material to be considerably larger than the main-anode spacing d, and also such that the starting-anode has a considerably smaller breakdown-voltage with respect to the cathode than -the breakdown-Voltage between the two `main electrodes.

2. The invention as defined in claim l, further characterized by Said breakdown-determining .means also including means for shielding the starting electrode against breakdown between itself and the main anode.

3. The `invention as dened in claim 1, characterized by said cathode'comprising a porous .terized'by'means for maintaining a portion ci `said cathode at an operating temperature which is lower than any other temperature within the device'whereby to determine the vapor-pressure p of the device.

5. The invention as dened in claim 4, further characterizedrby said coolest-point temperaturemaintaining means comprising a cooling-means for directly cooling the vaporizable reconstructing cathode-material, and -further characterized by the thickness of Lthe vaporizable reconstructing cathode-material being yas small as practicable whereby to obtainv only a small temperature-drop between the active cathode-surface and said cooling-means.

6. The invention as deined in claim 1, characterized by said starting electrode being above the yactive surface of said vaporizable reconstructing cathode-material.

7. The invention as denned in claim 1, characterized by said starting electrode being below the active surface of Ysaid Vaporizable reconstructing cathode-material.

8. The invention as deiined in claim 1, characterized by the main anode having a re-entrant portion extending into the device, and said active main-anode portion having a hole therein, and said starting-anode supporting-means comprising a closed-top chimney extending up from said hole.

9. The invention as defined in claim 8, and temperature -maintaining means comprising 'means for circulating a cooling-uid -nrst into heat-exchanging relation to the cathode, and then into said re-entrant'portion of vthe main anode into heat-exchanging relation with said active main-anode portion, `and -thenceout of the-device.

1C. The inventionas-dened inclaim 1, characterized by the main anode-having a re-entrant portion extending into the device, andtemperature-maintaining ymeans comprising -means for circulating a cooling-fluid -rst into heat-exchanging relation toithe cathode, andthenrinto said -re-entrant portion ofthe main anode into heat-exchanging relation with said activevmainanode portion, and/thence outof the device.

11. The invention fas deiined in claim 10, in combination with heating-means for heating the insulators for said main and starting anodes, respectively.

12. The inventionas denediin claim 1; characterized by said vaporizable reconstructing cathode-material being selected from the group comprising mercury, cadmium, cesium, rubidium and potassium.

13. vThe invention as dened in claim l, characterized by said vaporizable reconstructing cathode-material being a metal capable of forming a liquid pool ata reasonable temperature, and also having a loW-arc-drop characteristic.

14. The invention'as defined in claim 1,char acterized by said vaporizable reconstructing cathode-material being selected from the group comprising cesium, rubidium and potassium.

15. The invention asdefined in claim 14, further characterized by said breakdown-determining means also including means for shieldingthe starting electrode against breakdown between itself and the main anode.

16. The inventionas dened in claim 14, further characterized by said cathode comprising a. porous substantially non-vaporizable material holding at least a portion of said vaporizable reconstructing cathode-material, whereby the necessary quantity of vaporizable reconstructing cathode-material is reduced.

17. The invention as dened in claim 14, further characterized by said cathode comprising a porous substantially non-vaporizable material holding at least a portion of said vaporizablereconstructing cathode-material, and further characterized by the main-anode spacing d being small enough so-that operational difiicultieswould have been encountered due to droplets of the vaporizable reconstructing cathode-material Vbut for said porous material.

18. The invention as denned in claim 14, further characterized by means for maintaining a portion of said ca'tho'de'at an operating temperature which is lower than any other temperature within the device whereby to determine the vaporpressure 'p 0f the device.

19. The invention as defined in claim 14, further characterized by said coolest-point temperature-maintainingmeans comprising a cooling-means for directly cooling the vaporizable reconstructing cathode-material, and further charcterzed by the thicknessof-thc vaporizable reconstructing cathode-material'being as small as practicable whereby to obtainonlya small temperature-drop between the active cathode-surface a'ndsaid cooling-means.

20. The invention as defined in claim l4,.fur ther characterized `by a metal internal-surface 17 portion of the device, other than the active part of the cathode-pool, being beryllium-coated.

21. The invention as dened in claim 14, in combination with an insulatedly supported beryllium-coated grid interposed between the two main electrodes.

22. The invention as dened in claim 14, further characterized by a metal internal-surface portion of the device, other than the active part of the cathode-pool, being titanium.

23. The invention as defined in claim 14, in combination with an insulatedly supported grid having a titanium surface interposed between the two main electrodes.

24. The invention as defined in claim 1, characterized by said vaporizable reconstructing cathode-material being a stable alkali-metal having more than three shells in its atomic structure.

25. The invention as defined in claim 24, further characterized by said breakdown-determining means also including means for shielding the starting electrode against breakdown between itself and the main anode.

26. The invention as defined in claim 24, further characterized by said cathode comprising a porous substantially non-vaporizable material holding at least a portion of said vaporizable reconstructing cathode-material, whereby the necessary quantity of vaporizable reconstructing cathode-material is reduced.

27. The invention as dened in claim 24, further characterized by said cathode comprising a porous substantially non-vaporizable material holding at least a portion of said vaporizable reconstructing cathode-material, and further characterized by the main-anode spacing d being small enough so that operational diiculties would have been encountered due to droplets of the vaporizable reconstructing cathode-material but for said porous material.

28. The invention as dened in claim 24, further characterized by means for maintaining a portion of said cathode at an operating temperature which is lower than any other temperature 18 within the device whereby to determine the vaporpressure p of the device.

29. The invention as dened in claim 24, further characterized by said coolest-point temperature-maintaining means comprising a cooling-means for directly cooling the vaporizable reconstructing cathode-material, and further characterized by the thickness of the Vaporizable reconstructing cathode-material being as as small as practicable whereby to obtain only a small temperature-drop between the active cathode-surface and said cooling-means.

30. The invention as dei-ined in claim 24, further characterized by a metal internal-surface portion of the device, other than the active part of the cathode-pool, being beryllium-coated.

31. The invention as dened in claim 24, in combination with an insulatedly supported beryllium-coated grid interposed between the two main electrodes.

32. The invention as defined in claim 24, further characterized by a metal internal-surface portion of the device, other than the active part of the cathode-pool, being titanium.

33. The invention as dened in claim 24, in combination with an insulatedly supported grid having a titanium surface interposed between the two main electrodes.

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